[PATCH] use monotonic clock on Ruby 2.1+

[Eric Wong <e@80x24.org>]

The monotonic clock is immune to stepping adjustments so it is
more suitable for tracking elapsed time differences.
Process.clock_gettime also generates less garbage on 64-bit systems
due to the use of Flonum.
---
 bin/dtas-console    |  3 ++-
 lib/dtas.rb         | 12 ++++++++++++
 lib/dtas/process.rb |  2 +-
 3 files changed, 15 insertions(+), 2 deletions(-)

diff --git a/bin/dtas-console b/bin/dtas-console
index 18fe7d2..9fa4d09 100755
--- a/bin/dtas-console
+++ b/bin/dtas-console
@@ -3,6 +3,7 @@
 # License: GPLv3 or later (https://www.gnu.org/licenses/gpl-3.0.txt)
 #
 # Note: no idea what I'm doing, especially w.r.t. curses
+require 'dtas'
 require 'dtas/unix_client'
 require 'dtas/rg_state'
 require 'dtas/sigevent'
@@ -135,7 +136,7 @@ begin
         Curses.addstr(current['command'])
       end
 
-      elapsed = Time.now.to_f - current['spawn_at']
+      elapsed = DTAS.now - current['spawn_at']
       if (nr = cur['current_initial']) && (current_format = current['format'])
         rate = current_format['rate'].to_f
         elapsed += nr / rate
diff --git a/lib/dtas.rb b/lib/dtas.rb
index 9fc7253..f11d549 100644
--- a/lib/dtas.rb
+++ b/lib/dtas.rb
@@ -1,6 +1,18 @@
 # Copyright (C) 2013-2015 all contributors <dtas-all@nongnu.org>
 # License: GPLv3 or later (https://www.gnu.org/licenses/gpl-3.0.txt)
 module DTAS # :nodoc:
+  # try to use the monotonic clock in Ruby >= 2.1, it is immune to clock
+  # offset adjustments and generates less garbage (Float vs Time object)
+  begin
+    ::Process.clock_gettime(::Process::CLOCK_MONOTONIC)
+    def self.now
+      ::Process.clock_gettime(::Process::CLOCK_MONOTONIC)
+    end
+  rescue NameError, NoMethodError
+    def self.now # Ruby <= 2.0
+      Time.now.to_f
+    end
+  end
 end
 
 require_relative 'dtas/compat_onenine'
diff --git a/lib/dtas/process.rb b/lib/dtas/process.rb
index 5be107f..8c5e8e9 100644
--- a/lib/dtas/process.rb
+++ b/lib/dtas/process.rb
@@ -51,7 +51,7 @@ module DTAS::Process # :nodoc:
 
     pid = spawn(env, cmd, opts)
     warn [ :spawn, pid, cmd ].inspect if $DEBUG
-    @spawn_at = Time.now.to_f
+    @spawn_at = DTAS.now
     PIDS[pid] = self
     pid
   end
-- 
EW